The present invention relates to a polarization beam splitter for guided light.
It is used in the field of integrated optics, e.g. in connection with optical fiber sensors or transducers (e.g. electrical field sensors and temperature sensors), as well as in the coherent transmission of information by monomode optical fibers, or in the field of optical gyroscopes. In such fields, the polarization state of the optical waves used is a very important parameter.
In such fields, polarization beam splitters or simply beam splitters are essential devices permitting the spatial separation of the transverse electric TE and transverse magnetic TM modes from the optical waves used.
Various guided light polarization splitters are already known, which are produced on uniaxial electrooptical materials and in particular on LiNbO.sub.3 :Ti. On the latter material, whose crystallographic axes are conventionally designated X,Y and Z, the X and Y axes both correspond to the ordinary index of the material, whilst the Z axis corresponds to the extraordinary index of said material. It has already proved possible to produce:
directional couplers in propagation configurations along the X axis or Y axis (cf. document (1) which, like the other documents referred to hereinafter, is detailed at the end of the description),
devices using two-mode interference methods (cf. document (2)),
structures with Y-junctions (cf. document (3)) and splitters having ion exchange waveguide parts (cf. document (4)).
In addition, document (5) discloses a polarization splitter, which is diagrammatically shown in FIG. 1. This known splitter comprises a phase shifter 2 interconnecting two 3 dB directional couplers 4 and 6. By appropriately polarizing this known splitter, it is possible to respectively obtain at the two outputs 8 and 10 of the coupler 6 the TE and TM modes of an input light wave, which arrives at one 12 of the two inputs of the coupler 4.
This known splitter suffers from the disadvantages of requiring a Mach-Zehnder interferometer using a passive phase shifter which, introduces between the guides an identical phase shift for the two polarizations TE and TM, such a passive phase shifter being e.g. obtained by a local modification of the width of the optical guide, as will be shown hereinafter, while it also does not make it possible to eliminate the phase displacements which occur between the two output waves of the couplers 4 and 6, when action takes place on said assumed active couplers to bring them into the 3 dB state.